1. Field of the Invention
The present invention relates to methods for reducing turbidity and/or contamination in laundry waste water by treating the water with an effective amount of a first polymer comprised of dimethyl diallyl ammonium chloride (DMDAAC) and a dialkyl diallyl ammonium monomer (DADAAX) other than DMDAAC, and a second copolymer which is either an anionic, nonionic or cationic acrylamide polymer.
2. Description of the Background Art
The character of waste water generated by an industrial laundry is in large part a function of the customer group that the laundry serves. This customer group typically includes a wide variety of industrial and commercial firms including but not limited to heavy manufacturing industries, the electroplating and automotive industries, battery manufacturers, the service industries, newspapers, printers, auto garages, schools, and commercial and retail businesses. Because of these diverse customers, a wide variety of contaminants are present in the waste water of a typical laundry. Representative of the contaminants are oils and greases, heavy metals such as lead, cadmium or zinc, suspended solids such as dirt, hydrocarbon solvents, organic materials and others. Waste water from industrial laundries further includes in its complex mixture the soaps and surfactants used for cleaning; it also generally has high Biological Oxygen Demand (BOD), high Chemical Oxygen Demand (COD) and an alkaline pH. The range of constituents, as well as the variability that exists in laundry wastes, makes it a unique waste water to treat. Laundry waste water is also unique in that most contaminants enter the waste water not as a result of intrinsic processes or raw materials, but rather as residual materials discharged from the garments, shop towels, and other dust control items used by the laundries' customers.
Discharge of this laundry waste water to a municipal Publicly Owned Treatment Works (POTW) presents a significant problem to commercial laundries that generate large volumes of waste water containing the types of contaminants listed above. A typical industrial laundry has 20,000 to 200,000 gallons per day of discharge water. This can typically represent about 0.2% of the hydraulic load on a municipal treatment plant, yet at the same time represent 15 to 20% of its treatment load. In order to comply with local and federal discharge requirements, it is therefore often necessary to treat laundry waste water prior to discharge of the water to POTW. Typically, such waste is treated by adding effective amounts of chemical coagulation and/or flocculation agents, which causes a major part of the colloidally dispersed solids and oils in the water to be transformed together with the coagulants and/or flocculants into an easily separable form, mostly into a non-slimy flocculant deposit. Dissolved air floatation (DAF) is then typically used to separate the flocculant solids from the water phase. Vacuum filtration, pressure filtration or belt press filtration can be used to further dewater the floated solids.
The response of an individual waste water to a polymeric treatment additive is a complex function of the water's physical and chemical composition including, for example, the chemical composition of dispersed solid phases, the types of oils and greases, the average particle size, the size distribution of all dispersed phases, the washing chemicals and their concentrations, the temperature, the pH, etc. Added to this complexity is the presence of microorganisms that change the character of the system with time.
The terms coagulation and flocculation, as used herein, collectively refer to the separation of suspended solid particles from aqueous systems. This generally occurs by neutralizing the charge of the particles (coagulation), followed by agglomeration of the neutralized solids (flocculation).
Turbidity, as used herein, is defined as the cloudiness or haziness of a solution caused by finely suspended particles. Turbidity is measured using nephelometric turbidity units (NTU). As used herein, low turbidity suspensions are those generally having a low solids concentration (on a weight basis), i.e., a solids weight percent of 0.1 or less. This typically corresponds with an approximate turbidity of 50 NTU's or less, but may vary due to the nature of the solids or dissolved colored matter. High solids suspensions include those systems containing in excess of 0.1 weight percent suspended solids, which generally corresponds to a turbidity of greater than 50 NTU's. The present invention, while useful in water of any turbidity, is particularly directed to waters having a high turbidity.
From an ecological and economic viewpoint, the treatment of laundry waste water represents a problem of constantly increasing importance and numerous methods of treating this waste water are reported. For example, U.S. Pat. No. 5,076,937 describes a method for removing impurities such as the oil and grease associated with a pH activated surfactant from waste water by deactivating the surfactant to cause release of these impurities, infusing a gas into the solution, coalescing the oil and grease droplets with the gas to achieve droplet buoyancy, forming a layer of said droplets atop said solution, removing said layer and adjusting the pH of the solution to about neutral.
U.S. Pat. No. 4,198,294 discloses a method of reclaiming waste water by emulsifying the water with a high molecular weight anionic surface active oil, breaking the emulsion thereby producing a coherent flocculant which occludes the insoluble matter suspended in the water, and separating the flocculant from the purified water.
U.S. Pat. No. 4,108,768 discloses a method of purifying industrial waste waters by adjusting the pH of the water to at least 11.6, adding calcium chloride to flocculate oil or grease in the water, adding a coagulant to agglomerate the flocculant, and removing the flocculant.
Canadian patent 2124301 discloses a demulsifier comprising a hydrophobic polyelectrolyte copolymer comprising DMDAAC and a hydrophobic monomer. The hydrophobic monomer disclosed in this patent is selected from a group consisting of a quaternized dialkylaminoalkyl methacrylates and alkyl esters of (meth)acrylic acids, and not DADAAX as taught by the present invention. Moreover, while the patent is directed to waste water in general it does not specifically delineate efficacy in laundry waste water.
None of these methods for laundry waste water purification suggests the methods of the present invention, however.
Other treatments of laundry waste water include treating the water with a cationic polymer such as poly dimethyl diallyl ammonium chloride (poly DMDAAC), to destabilize the colloidal solids, followed by addition of a high molecular weight anionic or cationic acrylamide copolymer. The inventors have discovered that using a cationic copolymer of DMDAAC and another DADAAX followed by the addition of a high molecular weight anionic or cationic acrylamide copolymer results in an unexpected reduction of turbidity and contamination in the final settled water.
Because of the importance of reducing contamination in laundry waste water prior to discharge, there remains a very real and substantial need for improved methods of treating laundry waste water.